The incorrect positioning of teeth or the misalignment of teeth between the upper dental arch and lower dental arch are known as malocclusions. Dental health professionals generally categorize malocclusions into three classifications designated as Class I, Class II, and Class III. Class I malocclusions are those in which the individual teeth are not aligning well with each other and/or corresponding teeth in the opposite jaw, for example due to spacing or crowding problems. Class II malocclusions relate to those cases in which the upper jaw is not properly positioned relative to the lower jaw, resulting in the upper teeth projecting in front of the lower teeth. The excess horizontal overlap of upper teeth to the lower teeth in this type of malocclusion is typically referred to as excess overjet. Class III malocclusions occur when the lower jaw is positioned too far forward with respect to the upper jaw. This type of malocclusion is typically referred to as an underbite.
The most frequently treated type of malocclusion is the Class I malocclusion. Historically, practitioners treated Class I malocclusions by applying braces to a patient's teeth. This involves placing brackets on individual teeth and connecting the brackets with an archwire to guide movement of the teeth into desired alignment. More recently, removable alignment devices have entered the marketplace as a substitute for the traditional fixed-style braces. These removable alignment devices are designed to be placed over a patient's teeth and have teeth-receiving cavities shaped to receive and apply a resilient positioning force to the patient's teeth. Over a course of treatment, a series of preformed aligners are provided that gradually move the location of the teeth-receiving cavities and, correspondingly, the patient's teeth until the teeth are in a desired alignment. One of the most commercially successful versions of this removable alignment type device is sold under the tradename Invisalign®.
While both fixed braces and removable aligners are suitable for correcting Class I malocclusions, the devices cannot be used alone to correct Class II and Class III malocclusions. Rather, additional orthodontic appliances must be used to force the jaw into its proper bite position by forcing the jawbones and muscles to physically adjust to the proper bite position. For patients wearing fixed braces, the brace hardware can provide an architectural platform for attaching springs, rubber bands, or other appliances that apply a force to move the upper jaw and lower jaw into proper relative alignment. This architectural platform is not present on patients undergoing treatment with a removable aligner system. Moreover, because the aligners for these patients are designed to be removable, any supplemental correction forces applied to the aligners such as traditional orthodontic elastics can have a tendency to pull the aligners away from a patient's teeth, limiting the effectiveness of the treatment.